Inspection unit

ABSTRACT

Known inspection units ( 10 ) respectively have at an entrance and often at an exit of a radiation tunnel a radiation-shielding curtain ( 13 ) so that no ionized radiation can exit from the inspection unit ( 10 ) as a luggage piece or another object to be inspected is passed into or out of the inspection unit.  
     Contrary thereto, the solution described herein arranges, instead of individual curtains ( 13 ) of flexible lead cloths with high weight (G) which cause a great hindrance to flow of a luggage piece ( 7, 17 ), a plurality of light curtains ( 3 ) arranged at a spacing (a) one behind the other, so that the coefficient of fiction (μ) is smaller than when the heavier curtain ( 13 ) is used.

[0001] This invention concerns an inspection unit having a radiation tunnel as set forth in the preamble of claim 1.

[0002] Such a known inspection unit has, particularly at an entrance of the radiation tunnel, a radiation-shielding curtain so that when a luggage piece or other object to be inspected is fed into the inspection unit no ionized radiation can exit at this area. A radiation-shielding curtain is respectively mounted therefor at at least a front area of the radiation tunnel of the inspection unit, and also often at a rear area thereof if an exit of the tunnel is open when the object is ejected. Such a radiation-shielding curtain is normally of a plurality of downwardly-hanging, thick, lead cloths, which are mounted immediately adjacent to one another in a row.

[0003] Because of introduction of new x-ray protection regulations and a reduction in radiation threshold values associated therewith, additional shielding measures are necessary in such inspection units. Previously-used lead cloths and curtains of lead-containing material even today often quite substantially impair the flow of luggage pieces by application of friction, depending upon the weight of these curtains. Additional shielding for achieving smaller threshold values mean an increase of this weight because of an increased lead content in the shielding material. A greater weight of a curtain causes, however, a higher resistant force of the curtain that negatively affects the luggage pieces.

[0004] It is, therefore, an object of this invention to provide a radiation shielding apparatus in a zone of a radiation tunnel of an inspection unit that meets the new tightened threshold values and, nevertheless, assures an unimpaired transport through the inspection unit.

[0005] This object is met by the limitations of claim 1.

[0006] According to principles of the invention, instead of arranging a single curtain of flexible lead cloths with great weight that cause a significant hindrance of flow of luggage pieces, a plurality of light curtains are arranged at a particular spacing, one behind the other, so that the friction force is smaller than when a heavier curtain is employed.

[0007] By employing double-staggered curtains no increased resistance force is caused if the spacing of the light-in-weight curtains is approximately the length of the front-most curtain. A minimal spacing of the curtains should, however, not be less than half the length of the front, up-stream, curtain.

[0008] In further carrying out the invention, it is beneficial for the curtains to additionally be coated with a material having a particularly small friction value.

[0009] The invention is described in more detail using drawings of an embodiment. Shown are:

[0010]FIG. 1 is a prior-art radiation shielding apparatus in an inspection unit;

[0011]FIG. 2 is a representation of forces on a lead curtain;

[0012]FIG. 3 is a radiation shielding apparatus of this invention.

[0013] A radiation shielding apparatus of the prior art is shown in FIG. 1. An inspection unit 10 has respectively at each of an entrance and an exit of a radiation tunnel 12 a shielding curtain 13. Between the two shielding curtains 13 there is a radiation zone 14 in which there is at least one radiation source 15 with at least on(e detector arrangement 16 directed toward it. A transport system 18, which is part of the inspection unit 10, extends through the radiation tunnel 14. A luggage piece 17 to be transported through the inspection unit 10 lies on the transport system 18. During transport, this luggage piece is subjected to a resistance force W of the curtain 13.

[0014] This resistance force W is thereby proportional to a tension force S of the curtain 13:

W˜S cos α.

[0015] The tension force S is determined according to the following formula

S=G(1+e ^(μα)),

[0016] where G is the weight of the curtain 13 (acting at a point), the symbol μ is the coefficient of friction and the α-symbol is the looping angle of grip.

[0017]FIG. 2 shows this interrelationship diagrammatically.

[0018] With a reduction in the radiation threshold values, and a corresponding increase in shielding values for the reduced radiation values, according to the prior art the weight G of the curtain 13 would have to be increased. If the weight G were only doubled, however, a resistance force W increase by a factor of 7.39 would result. This would, in turn, greatly influence the flow of the luggage piece 17.

[0019] A new type of radiation shielding apparatus in an inspection unit 1 is shown in FIG. 3. The radiation shielding apparatus includes a plurality of light-in-weight lead curtains 3, in this case four, arranged here in pairs with one being spaced behind the other, in the radiation tunnel 2 of the inspection unit 1. The two front functionally-cooperating lead curtains 3 are mounted within the radiation tunnel 2 in front of a radiation zone 4, with the two rear functionally-cooperating lead curtains 3 being behind this radiation zone 4. There is at least one radiation source 5, with at least one detector arrangement 6 directed toward it, in the radiation zone 4. A transport system 8, for example a slide belt conveyer, is included in the inspection unit 1 for transporting a luggage piece 7 in and through the radiation tunnel 2.

[0020] Each of the lead curtains 3 has a substantially smaller individual weight G than does the curtain 13 of FIG. 1, because it is made thinner. The thickness “d” of the lead curtains 3 that determines the weight G is dependent on the intensity of the radiation sources 5, 15 (dose, power) and the radiation values associated therewith. By setting the maximum allowable radiation value, the required shielding of the radiation tunnel 2, 12 is determined. A lead-equivalent value can serve as a prescribed shielding number. If the lead-equivalent value is higher, the intensity of a released radiation is lower. By using only one curtain 13 as shown in FIG. 1, a lead-equivalent value, for example, of 0.35 mm requires an approximately 2 mm thick curtain 13. By using two or more functionally cooperating lead curtains 3 mounted in front of and behind the radiation zone 4, this thickness of 2 mm can be distributed to the individual lead curtains. If there are, for example, two lead curtains 3 arranged before and after the radiation zone 4, each of the lead curtains 3 then only has a thickness of 1 mm, for three lead curtains 3, each only has a thickness d of 0.66 mm and for four lead curtains 4 each only has a thickness d of 0.5 mm. Thus, the weight G of the individual lead curtains 3 is reduced, depending on the number included in the inspection unit 1.

[0021] Even if the lead-equivalent value is at 0.7 mm, this can be distributed without problems by using additional lead curtains 3. It is, however, also possible within the framework of a permissible resistance force W, to distribute this lead-equivalent value by determining a new thickness value d for the individual lead curtains 3.

[0022] In addition to the thickness d, the length L of the lead curtains 3 influences the weight G of the individual lead curtains 3. This length L is mainly determined by a height h of the radiation tunnel 2.

[0023] In a particular embodiment the weight G of the second, third, forth and further additional lead curtains 3 can be further reduced by making those lead curtains 3 positioned between the two outermost lead curtains 3 shorter. It is important that the outermost lead curtains 3, those screening the entrance and the exit of the radiation tunnel 2, reach to the transport system 8.

[0024] A spacing “a” of the pair-wise mounted lead curtains 3 between one another in the embodiment, is approximately a length L of the respective front lead curtain 3. In this regard, however, the lead curtains 3 lying therebetween should have a minimal spacing a_(min) of no less than half the length L, because otherwise, again, an increase of the resistance force W results when a luggage piece 7 simultaneously comes into contact with multiple lead curtains 3.

[0025] In a further enhancement, it is provided that the lead curtains 3 are covered with a material having a particularly small coefficient of friction μ. The individual lead curtain 3 can be of one entire cloth or of slightly overlapping lead cloths. 

I claim:
 1. Inspection unit with a radiation tunnel in which a radiation zone is defined by at least one radiation source with at least one detector arrangement directed toward it, there being at least one entrance which is shielded outwardly by a radiation shielding apparatus, characterized in that: the radiation shielding apparatus comprises at least two functionally-cooperating curtains (3) arranged at a spacing (a), one behind the other, in front of the radiation zone (4) in the radiation tunnel (2).
 2. The inspection unit of claim 1 characterized in that at least two functionally cooperating curtains (3) are arranged at a spacing (a), one behind the other, following the radiation zone (4) in the radiation tunnel (2).
 3. The inspection unit of claim 1 or 2 characterized in that the spacing (a) between the cooperating curtains (3) corresponds approximately to the length of the first-most curtain.
 4. The inspection unit of claim 3 characterized in that the spacing is not less than a minimal spacing (a_(min)) between the curtains (3) of one half the length of the leading curtain.
 5. The inspection unit of one of claims 1 through 4 characterized in that the curtains (3) positioned between the curtain (3) of the radiation-tunnel (2) entrance and the radiation zone (4), and the curtain (3) of the radiation-tunnel (2) exit and the radiation zone (4), are shorter than these outermost curtains (3).
 6. The inspection unit of one of claims 1 through 5 characterized in that the curtains (3) are additionally covered with a material having a particularly small coefficient of friction (μ).
 7. The inspection unit of one of claims 1 through 6 characterized in that the curtains (3) are of thin slightly-overlapping lead cloths.
 8. The inspection unit of one of claims 1 through 6 characterized in that the curtains (3) are thin whole-piece lead curtains. 